1. Field of the Invention
The present invention relates generally to wire stranding machines, and more particularly, to an automatic, single-twist stranding machine having a reciprocating flyer and improved control means for increased lay length accuracy and greater uniformity of the layers of wire wound on the reel.
2. Prior Art
Machines for twisting a plurality of wires into a single twisted wire bunch and winding the same onto a reel are well known. One such machine is described in U.S. Pat. No. 2,817,948 issued to Cook. The Cook stranding machine comprises a rotatable flyer and a reciprocally traversing reel rotatably supported within the flyer. A differential exists between the rate of rotation of the flyer and reel. A plurality of wire strands are fed from sources, external to the machine, to the flyer for twisting the strands together. Due to the differential in rotation rates, the twisted strands are then wound from the flyer onto the reel. Moreover, because the even layers thereon.
It is well known that, in order for the lay length (i.e., the length of each twist) to be kept constant, a fixed length of the wire strands must enter the machine for each rotation of the flyer. The length of wire which enters the machine during each rotation of the flyer depends upon the velocity of between the flyer and reel, and (ii) the instantaneous diameter of the combined reel and wound wire (referred to hereinafter as the "effective diameter" of the reel).
It is well known that, as the effective diameter of the reel increases, the tangential velocity of the wire winding circumferentially onto the reel will tend to increase, notwithstanding a fixed rate of rotation of the reel. Therefore, in order to maintain a constant lay length, it is necessary to reduce, continually, the rate of rotation of the reel to compensate for the continually increasing effective diameter thereof, as twisted wire is wound thereon. The Cook machine disclosed in U.S. Pat. No. 2,817,948 includes a means for periodically reducing the rate of rotation of the reel by means of an adjustable pulley mounted on a shaft 59 which is coupled to the reel shaft. The surface of the adjustable pulley, which is in contact with a drive belt, can be manually varied so as to change the effective diameter of the pulley, thereby adjusting the speed of shaft 59. By so adjusting the speed of shaft 59, the speed of the reel shaft coupled thereto can be controlled. As indicated above, the control sought is a reduction of the reel's rate of rotation as the effective diameter thereof increases, in order to maintain a fixed wire velocity.
Although the Cook stranding machine was an improvement over earlier machines known to the prior art, it nevertheless fails to overcome several significant limitations and shortcomings of the prior art. For example, by reciprocating the reel within the flyer (the so-called "closed flyer"), the Cook machine tends to vibrate excessively as do earlier stranding machines. This is due to the fact that the distribution of the wire being wound onto a reciprocating and rotating reel is not perfectly uniform, causing a non-uniform weight, or out-of-balance, condition. The present invention overcomes this shortcoming by providing means for reciprocating the flyer with respect to a non-reciprocating reel. The flyer can be more accurately balanced, and the balance, once attained, is permanent and independent of wire buildup on the reel. Thus, this invention achieves a substantial reduction of vibration. In addition, the innovative feature of reciprocating the lighter flyer enables (i) the use of drive motors and bearings which are smaller and less expensive than those required for driving heavier reels, especially when loaded; and (ii) operation at higher speeds than possible with machines of the prior art.
A second significant shortcoming of the prior art, which is not eliminated by the Cook machine disclosed in U.S. Pat. No. 2,817,948, relates to the removal of loaded reels after a stranding, twisting and winding cycle is completed. In the prior art, reel removal is typically accomplished by positioning a hoist over the machine and lifting the reel upward and then to the side so that reel may be lowered to ground level. This is a slow process and one which requires the utilization of hoist means the space within which to move and operate the hoist. The present invention has overcome this shortcoming of the prior art by providing means for conveniently pivoting, i.e., lowering, the reel of wire from its take-up position to one approximately 90.degree. removed therefrom, which is close to floor level. The foregoing pivotability of the reel support structure is enabled by the fact that the reel's support structure is not mechanically interconnected to means for reciprocating the rotating reel, as is the case with respect to prior art machines.
One of the reasons that stranding machines of the prior art did not utilize reciprocating flyers and stationary reels is that a reciprocating flyer tends to place pulling forces on the wire strands passing therethrough, as the traversing flyer reverses its direction. This tends to cause an accumulation of the wire strands as they pass through the flyer and, as a consequence thereof, a corresponding variation in the length of wire wound during each flyer revolution. When the latter length is varied, the lay length of the bunched wire is, by definition, likewise varied, resulting in an undesirable lack of uniformity of the lay length. The lay length control means known to the prior art lack the accuracy and responsiveness necessary to correct for any wire velocity variations introduced by a reciprocating flyer. However, the present invention comprises a closed loop, servo-actuated lay length control means which enables the lay length to be controlled to an accuracy heretofore not known to the art. By virtue of such control means, the advantages obtainable from a machine in which the flyer reciprocates with respect to a stationary reel, instead of vice versa, have been achieved; i.e., the reduction of vibration, the suitability of smaller and less expensive drive motors and bearings, and the drop-out, pivotable reel. In addition, the improved lay length control and reduction of vibration enable winding operations to be carried out at speeds higher than heretofore possible, withiout sacrificing, to any commercially significant degree, the uniformity of the lay length of the resulting bunched and twisted wire strands.
In many applications, wire having a highly uniform lay length is required. It is apparent from the design of the Cook machine disclosed in U.S. Pat. No. 2,817,948, that it is incapable of twisting the wire strands with a precise lay length, especially when small gauge wire is being used. This is because the reel speed is controlled by means of the above-described configuration. Such adjustable pulleys inherently lack the capability to maintain a constant drive ratio, because the diameter of the contacting pulley surface will vary with drive belt wear and tension. Inasmuch as the adjustable pulley and drive belt ultimately drive the reel shaft, the rate of rotation of the reel, and consequently the lay length of the wire, will also vary with belt wear and changes in tension.
A further disadvantage of the variable pulley control means taught by Cook is that only approximately 8% of the surface of the drive belt is in contact with the surface of the adjustable pulley, a condition which furthers the wearing out of the belt, which in turn, increases maintenance costs and machine down-time. Moreover, and perhaps more importantly, with only about 8% of the drive belt surface in contact with the variable pulley, a very inadequate dynamic range is provided for control of the rotation rate of the reel, from its unloaded to its fully loaded condition. This deficiency is further compounded by the fact that the Cook machine disclosed in U.S. Pat. No. 2,817,948 is one which is manually operated by an attendant looking at a speedometer measuring the velocity of the wire strands being fed into the machine. As the lineal wire velocity increases, due to the increasing effective diameter of the reel, the attendant, observing the same, periodically rotates a shaft which varies the adjustable pulley. In this manner, the reel speed is reduced, and therefore, the speed at which the wire is being pulled into the machine. Thus, in addition to the inherent inaccuracy of the variable pulley and belt drive control means, and the inadequacy of its dynamic range, the lay length accuracy attainable by the above-cited Cook machine may be further reduced by the lack of skill and attentiveness of the attendant.
A second patent issued to Cook, U.S. Pat. No. 2,929,193, discloses various embodiments of an automatic speed control device which eliminates the requirement that an attendant periodically reduce the reel speed. Although the use of the Cook speed controls disclosed in the foregoing Cook patent eliminates the inaccuracy of lay length uniformity attributable to the attendant, the inherent inaccuracy of a variable pulley control means nevertheless remains.
With reference to the Cook machines disclosed in U.S. Pat. No. 2,929,193, attention is now directed to his means for generating the "error" signal which is coupled to, and adapted to adjust, the variable pulley and belt control means. In one embodiment, Cook uses a synchronous motor, as a reference, to drive a disk having electrically conducting studs extending outwardly therefrom. Rotating concentrically with the disk is a shaft 17 having an electrically conducting eccentric arm. The shaft 17 is driven by a pulley which is itself driven by a wire strand being fed into the machine; therefore, the rate of rotation of the shaft 17 is proportional to the velocity of the wire strand. As the effective diameter of the reel increases, the velocity of the wire increases, causing the shaft 17 to rotate faster, until the extended arm affixed thereto makes electrical contact with one of the conducting studs on the concentrically rotating disk. The electrical error signal generated is coupled to a servo motor which actuates the variable pulley-belt control means to slow the reel speed, and thereby to disengage the contacting stud and arm. The foregoing error signal generating means, while controlling the reel rate of rotation, is incapable of making corrections for variations in the rate of rotation of the flyer. It should be recalled that the achievement of uniform and accurate lay lengths requires that the length of wire pulled into the machine for each revolution of the flyer be maintained constant. If the flyer speed changes, the period of one rotation changes; consequently, the lay length changes correspondingly. On the above-described Cook control device, the error signal is generated whenever the reel speed reaches a predetermined level corresponding to the speed of the reference synchronous motor. Inasmuch as the fixed speed of the reference is unrelated to the flyer speed, the capability of the foregoing control means is inherently limited. On the other hand, the lay length control means disclosed in the present invention is responsive to variations in the speed of the flyer as well as to wire buildup on the reel, and therefore, it is capable of greater lay length control accuracy than that achievable by the foregoing Cook structure.
It should be noted further that Cook, in U.S. Pat. No. 2,929,193, discloses two embodiments for generating a mechanical error signal; i.e., an output shaft whose rate of rotation is an analog of the difference in speeds of the reel and the flyer. These embodiments, however, rely extensively on mechanical drives of the type having gears, teeth or cogs, which are inherently incapable of the fine adjustment required for twisting a precise lay length. Moreover, Cook's differential mechanisms comprise many mechanical parts, e.g., pinions, bevel gears, and a spur gear, which, in addition to introducing sources of error, are power inefficient and more costly than the means disclosed herein.
In order to wind the twisted strands onto the reel in uniform layers, it is important to accurately control the points at which the reciprocating member (reel or flyer) reverses with respect to the reel end flanges. If the reciprocating member does not reverse direction at a point exactly at an end flange of the reel, there will result either an accumulation of wire adjacent to this flange or a shortage of wire (or recess) in the vicinity of the flange. Such accumulations or recesses at the flanges are, of course, undesirable. The Cook patent does not disclose the means used in his stranding machine for controlling the points at which the reciprocating reel reverses. One arrangement well known in the prior art comprises stop or limit switches which are adjusted manually to determine the range of the reciprocating member. However, manual adjustment is time-consuming and requires considerable operator skill. Furthermore, take-up reel dimensions vary greatly, necessitating the readjustment of the stop or limit switches each time a new reel is mounted on the machine. The latter requirement is, of course, disadvantageous in high speed production applications.
U.S. Pat. No. 3,677,483, issued to Henrich, discloses a wire winding apparatus which automatically displaces the limit switches controlling the reversal of a reciprocating pulley 4 so as to obtain uniform layers of wire on a reel. Henrich's apparatus responds to changes in the tension of the wire as being indicative of irregular buildup. In his apparatus, the tension of the wire affects movements of a wire dancer or accumulator. This approach is unsuitable in standing machines wherein no change of wire tension necessarily occurs when the velocity of the wire being drawn into the machine changes due to irregular wire buildup on a reel. Moreover, it would be very difficult to adapt the Henrich apparatus for use in a wire stranding machine instead of the simple winding operation for which it is designed. This is because, in a stranding machine, both the flyer and the reel are rotating and consequently, there is no convenient means for sensing the wire tension at a point between the flyer and the reel. In contrast, in Henrich's apparatus, only the reel rotates as wire is fed over a non-rotating pulley 13.
The Henrich apparatus suffers from several other disadvantages which are not found in this invention. For one thing, movements of the dancer (pulley 13) can be caused by forces other than changes in wire tension due to irregular buildup. For example, movement may result from variations in the speed of the machine which supplies wire to the dancer.
A second disadvantage of Henrich's apparatus lies in the fact that the dancer movements may be sluggish, and therefore, unresponsive when a heavy mass is involved.
Thirdly, changes in wire tension are often caused by the dancer itself because it is spring-loaded; thus, the spring force may vary with the position of the dancer or with the geometry of the wire path as the dancer moves, thereby introducing spurious variations in wire tension.
A further shortcoming of Henrich's apparatus is that it cannot distinguish between a change in tension due to wire buildup or recess at the reel flange from a change due to other causes away from the reel flanges and unrelated to improper reversal points of the reciprocating pulley.
Lastly, Henrich's apparatus makes an adjustment of an apparently incorrect limit switch position upon sensing the change in tension, without any prior verification of the condition. Moreover, his apparatus does not limit the adjustment to predetermined spaced intervals to allow the limit switch to be moved before another adjustment is initiated. This may result in overcorrection.
As will be seen from the description below, the means for obtaining uniform layering of the wire on the reel, as taught by this invention, does not suffer from any of the foregoing shortcomings and disadvantages of the Henrich apparatus. Thus, it represents a significant advance in the art.